The present invention generally relates to so called composite type magnetic head assemblies for magnetic tape recorders, comprising a pair of magnetic heads provided on a single base body, one for recording and one for playback, or both for recording and playback, along a direction of tape transportation, and in particular to a composite type magnetic head assembly designed to provide an improved contact between the magnetic tape and the magnetic heads wherein a zigzag movement or lateral deviation of the magnetic tape during tape transportation when passing the tape through the magnetic head assembly is eliminated.
In a commonly used audio magnetic tape cassette such as the one called a compact cassette, a window is defined in the tape cassette so as to allow contact for the magnetic tape contained therein with a magnetic head of a tape recorder. In such a tape cassette, a pressure pad is provided in correspondence to the window for urging the magnetic tape to the magnetic head so as to maintain a stable contact between the magnetic tape and the magnetic head.
Conventionally, there is a tape recorder called three head-type tape recorder wherein three separate magnetic heads are used for recording, reproducing and erasing respectively. In such a tape recorder, it is necessary to design the magnetic head such that both of the recording head and reproducing heads make contact with the magnetic tape through the window in the tape cassette. For this purpose, a so-called composite type magnetic head assembly is commonly used wherein the recording head and the reproducing head are assembled as a unitary body such that the recording and reproducing heads are aligned adjacent to each other along a transport direction of the magnetic tape.
There are various modifications in the composite type magnetic head assembly. A typical example of such a composite type magnetic head assembly is the one used commonly for recording and playback of a two channel stereo signal on and from the magnetic tape having a four track format. Further, there is a composite type magnetic head assembly designed to record and reproduce an eight channel audio signals or data on and from the magnetic tape in an eight track format. In this type of magnetic head assembly, a pair of magnetic heads each carrying four magnetic cores thereon are mounted on a common base body adjacent to each other along the tape transport direction such that the four magnetic cores of the first magnetic head are disposed alternately to the four magnetic cores of the second magnetic head and such that there are eight tracks defined laterally on the magnetic tape. In the composite magnetic head assembly having such a construction, both of the magnetic heads are used for recording and for playback.
In such a composite type magnetic head assembly, the magnetic cores in each of the magnetic heads have to trace the corresponding tracks precisely. For example, in the composite type magnetic head assembly of the first mentioned type where a two channel stereo signal is recorded on the magnetic tape in the four track format, it is necessary that the magnetic core in the reproducing head traces the track defined by the magnetic core in the recording head exactly. For this purpose, there is a prior art construction (Japanese Laid-open Utility Model Application No. 56-2135) in which the recording head and reproducing head are held independently on a common base body such that the magnetic heads are adjustable in a lateral direction of the magnetic tape.
In this prior art construction, one of the magnetic heads such as the recording head is mounted on the base body via a base plate such that the position of the magnetic head is adjustable in the lateral direction of the magnetic tape. At the same time, the other of the magnetic heads such as the reproducing head is mounted directly on the base body. Further, the base body itself is held on a chassis or frame of the tape recorder by connecting screws such that the magnetic heads carried thereon can be rotated or tilted relative to the magnetic tape unitarily with the base body about a hypothetical axis which extends parallel to the tape transport direction. As a result of this, a tilt angle of the magnetic head is adjusted. Furthermore, by adjusting the screws in this prior art construction, it is possible to rotate the base body about another axis extending perpendicularly to a plane of the magnetic tape passing through the magnetic head assembly. As a result, the orientation of the magnetic head relative to the tape transporting direction in the plane of the magnetic tape or so called azimuth angle is adjusted.
In such a prior art composite magnetic head assembly, one can adjust the position and orientation of the magnetic heads such that gaps provided in the magnetic cores of the recording and reproducing heads trace an exactly identical track with a proper azimuth angle. However, such a prior art composite type magnetic head assembly has a problem in that the construction for mounting the magnetic heads on the chassis of the tape recorder is complex and there is a tendency that the mounting state becomes non-uniform in the recording head and in the reproducing head. When such a difference exists in the mounting state, the position and direction of a contacting surface provided on the magnetic head for guiding the magnetic tape contacting therewith tends to differ in the recording head and the reproducing head. In other words, the magnetic tape is guided in different directions in each of the magnetic heads and there is a substantial risk that the magnetic tape is transported zigzag across the composite magnetic head assembly or deviated laterally during the tape transportation. Such an unstable tape transport tends to appear also as a result of the adjustment of the magnetic heads performed independently to each other, as such an adjustment tends to invite disagreement in the guiding action of the contacting surfaces of the recording and reproducing heads.
Of course, these problems can be avoided when one uses a primitive composite magnetic head assembly where the recording and reproducing heads are fixed each other as a unitary body and there is formed a common contacting surface. In such a magnetic head assembly, however, it is not possible to adjust the magnetic heads independently and is disadvantageous for adjusting the gaps in the magnetic heads to trace an identical track on the magnetic tape.
When the tape transport becomes unstable, a uniform contact between the magnetic tape and the head is lost and there may be a fluctuation in the output level or dropout in the reproduced signal in the extreme case.